1. Technical Field
The invention relates to a process for recovering hydrocarbons from a subterranean hydrocarbon-bearing formation and more particularly to a hydrocarbon recovery process utilizing a permeability-reducing material.
2. Background Information
Fluid communication in the near well bore between a hydrocarbon production interval or a drive fluid injection interval and an underlying aquifer can diminish hydrocarbon recovery from the associated hydrocarbon-bearing formation. Fluid communication can occur either across permeable matrix separating the interval from the aquifer or via one or more vertical fractures or a fracture network connecting the interval and the aquifer.
When hydrocarbons are produced from a formation across a near well bore production interval into the well bore penetrating the formation, water from an underlying aquifer tends to migrate upward into the production interval if there is fluid communication between the interval and the aquifer. Migration of water into the production interval is termed water coning. There are two negative consequences of water coning. The first is that water residing in the production interval can block or significantly diminish the flow of hydrocarbons from the outlying formation into the well bore. The second consequence is that water production can compete with and diminish hydrocarbon production. As a result, the ratio of water to hydrocarbons produced from the well bore can become unacceptably high when water coning occurs.
Water coning is extremely difficult to remedy whether fluid communication between the interval and aquifer is across vertical fractures or matrix. A traditional method of treating water coning is to cement the well bore over the lower portion of the production interval. Unfortunately, well bore cementing at best only slightly reduces water coning and subsequent water production. Water coning usually recurs at the uncemented upper portion of the production interval shortly after the cement treatment, negating the effectiveness of the treatment.
Another means of treating water coning is to inject gels into the fractures or matrix providing fluid communication with the production interval. A gel treatment can block migration of aquifer water into the production interval, but the treatment also unacceptably damages the production interval because of the presence of gel in the interval. Even attempts at selective gel placement, such as mechanical zone isolation, are not entirely satisfactory because the gel tends to migrate into the production interval. Since it is difficult to place a gel using present technology to effectively prevent water coning without excessive damage to the production interval, known gel treatments have limited practical utility for the prevention of water coning.
The inverse problem to water coning exists where there is fluid communication between an underlying aquifer and a drive fluid injection interval. Hydrocarbon drive fluids are commonly injected into a hydrocarbon-bearing formation via the injection interval of an injection well bore to displace the hydrocarbons into an adjoining production well bore. Where fluid communication exists between the injection interval and the underlying aquifer, particularly in the near well bore, the drive fluid is undesirably diverted away from the outlying hydrocarbon-bearing zones of the formation into the underlying aquifer.
For the same types of reasons that gels are not suited for the treatment of water coning in a production interval, gels are unsuitable for treating the loss of drive fluid from an injection interval. When gels are used to plug fluid pathways between an injection interval and an aquifer, corresponding plugging of the injection interval is virtually unavoidable, even with zone isolation. As such, gel treatments unacceptably reduce injectivity into the injection well bore and reduce hydrocarbon production from the adjacent production well bore.
A treatment process is needed for selectively placing a permeability-reducing material in the lower portion of a near well bore production or injection interval in fluid communication with an underlying aquifer via permeable matrix or vertical fractures. A treatment process is further needed which does not significantly diminish fluid communication between the upper portion of the near well bore interval and an outlying hydrocarbon-bearing formation when the permeability-reducing material is placed in the lower portion of the interval.